The present invention relates to a display device which utilizes an emission of electrons into a vacuum, and more particularly, to a display device which can enhance the display characteristics by enabling the stable control of an electron emission quantity by forming a gap between electron emitting sources and control electrodes which control the electron emission quantity from the electron emitting sources with high accuracy.
As a display device which exhibits the high brightness and the high definition, color cathode ray tubes have been widely used conventionally. However, along with the recent request for the higher quality of images of information processing equipment or television broadcasting, the demand for planar displays (panel displays) which are light in weight and require a small space while exhibiting the high brightness and the high definition has been increasing.
As typical examples, liquid crystal display devices, plasma display devices and the like have been put into practice. Further, particularly, as display devices which realize the higher brightness, it is expected that various kinds of panel-type display devices including a display device which utilizes an emission of electrons from electron emitting sources into a vacuum (hereinafter, referred to as “an electron emission type display device” or “a field emission type display device”) and an organic EL display which is characterized by low power consumption will be commercialized.
Among such panel type display devices, as the above-mentioned field emission type display device, a display device having an electron emission structure which was invented by C. A. Spindt et al (for example, see U.S. Pat. No. 3,453,478, Japanese Laid-open Patent Publication 21305/2000), a display device having an electron emission structure of a metal-insulator-metal (MIM) type, a display device having an electron emission structure which utilizes an electron emission phenomenon based on a quantum theory tunneling effect (also referred to as “surface conduction type electron emitting source, see Japanese Laid-open Patent Publication 21305/2000), and a display device which utilizes an electron emission phenomenon having a diamond film, a graphite film and carbon nanotubes and the like have been known.
FIG. 38 is a cross-sectional view for explaining one constitutional example of a known field emission type display device. FIG. 39A and FIG. 39B are explanatory views showing constitutional examples of an electron emission source of one pixel and a control electrode which controls an electron emission quantity from the electron emission source, wherein FIG. 39A is a cross-sectional view and FIG. 39B is a plan view. The field emission type display device is constituted such that a sealing frame 300 is interposed to seal a space defined between both inner peripheries of a rear panel 100 which forms field-emission type electron emitting sources 2a and control electrodes 4 over an inner surface thereof and a face panel 200 which forms anodes 7 and fluorescent material layers 6 on an inner surface thereof which faces the above-mentioned rear panel 100, and the inside which is defined by the rear panel 100, the face panel 200 and the sealing frame 300 is reduced to a pressure lower than an atmospheric pressure of an external field or is evacuated (hereinafter referred to as “vacuum”).
The rear panel 100 includes cathode wires 2 which have electron emitting sources 2a and the control electrodes 4 which are formed such that the control electrodes 4 cross the cathode wires 2 by way of an insulation layer 3 on the rear substrate 1 preferably made of glass or alumina or the like. Then, an electron emission quantity (including turning on or off of emission) from the electron emitting sources 2a are controlled in response to the potential difference between the cathode wires 2 and the control electrodes 4.
Further, the face panel 200 includes the anodes 7 and the fluorescent material layers 6 on a face substrate 5 formed of light-transmitting material such as glass. The sealing frame 300 is fixedly secured to the inner peripheries of the rear panel 100 and the face panel 200 using an adhesive agent such as frit glass. The inside defined by the rear panel 100, the face panel 200 and the sealing frame 300 is evacuated to a vacuum of 10−5 to 10−7 Torr, for example.
With respect to this type of display device whose inside is evacuated, to hold a gap between the rear panel 100 and the face panel 200, that is, a gap between the cathode wires 2 (electron emitting sources 2a) and the anodes 7 at a predetermined value, it is necessary to provide gap holding members 9 at portions except for a pixel region.
The insulation layer 3 is interposed between the cathode wires 2 formed on the rear panel 100 and the control electrodes 4 which cross the cathode wires 2 and an hole (grid hole) 4a is formed at each crossing portion of the cathode wire 2 and the control electrode 4. The hole 4a allows electrons emitted from the electron emitting source 2a to pass therethrough toward the anode 7 side. On the other hand, the electron emitting source 2a is formed on the above-mentioned crossing portion of the cathode wire 2 and the control electrode 4 and the insulation layer 3 is eliminated at a portion which corresponds to the hole 4a of the control electrode 4. The above-mentioned electron emitting sources 2a are constituted of carbon nanotubes (CNT), diamond-like carbon (DLC) or other field emission cathode, for example.
Here, as the electron emitting sources 2a, electron emitting sources which use carbon nanotubes are illustrated. As shown in FIG. 39A and FIG. 39B, the electron emitting source 2a is formed right below the hole 4a of the control electrode 4. Although the case in which one electron emitting source 2a is formed per one pixel is illustrated in FIG. 39A and FIG. 39B, a plurality of electron emitting sources 2a may be formed per one pixel.
FIG. 40A and FIG. 40B are explanatory views corresponding to FIG. 39A and FIG. 39B which show a display device forming a plurality of electron emitting sources per one pixel. Here, a plurality of holes 4a are formed in the control electrode 4 and a plurality of electron emitting sources 2a are arranged on a cathode wire 2 corresponding to respective holes 4a. 
Electrons emitted from the rear panel 100 impinge on the fluorescent material layer 6 of the opposing face panel 200. Light which corresponds to the emitting characteristics of the fluorescent material layer 6 is irradiated to the outside of the face panel 200 so that a display device performs the function thereof.
As literatures which disclose the conventional technique related to this type of display device, for example, Japanese Laid-open Patent Publication 144652/1999, Japanese Laid-open Patent Publication 323078/2000 and the like are named.
FIG. 41 is an enlarged cross-sectional view of one pixel portion for explaining a constitutional example of a rear panel of a conventional field emission type display device. In such a display device of this type, with respect to a rear panel 100, cathode wires 2 are formed on a rear substrate 1 by a thin film patterning technique or the like, an insulation layer 3 having a given thickness is formed on the cathode wires 2, and the insulation layer 3 corresponding to pixel portions are removed. Then, control electrodes 4 are formed on the insulation layer 3 by a vapor deposition method or a sputtering method except for holes 4a. 
Since the insulation layer 3 is formed by coating resin material using a screen printing method, it is difficult to make a thickness of the insulation layer 3 uniform. Accordingly, it is impossible to obtain the uniform thickness with no irregularities over the entire surface of the display region. Since the control electrodes 4 are formed along the surface contour of the insulation layer 3, as emphasized in conjunction with FIG. 41, the irregularities are generated with respect to a gap defined between the cathode wires 2 and the control electrodes 4 due to the irregularities of the thickness of the insulation layer 3. It is necessary to control the gap between the cathode wires 2 and the control electrode 4 at a μm level because the irregularities of the gap in the peripheries of the holes 4a of the control electrode 4 bring about the irregularities of electron emission abilities of individual pixels.
Further, since the insulation layer 3 is disposed between the crossing portions of the cathode wires 2 and the control electrodes 4, the capacitance is generated. The irregularities of the thickness of the insulation layer 3 lead to the irregularities of the capacitance and when the thickness of the insulation layer 3 is increased, this obstructs the high-frequency driving. Accordingly, the thinner the thickness of the insulation layer 3, the high-frequency driving is improved and hence, it is ultimately desirable to have the constitution which can eliminate the insulation layer 3.
Then, in this type of display device, as has been explained in conjunction with FIG. 38, it is necessary to provide the gap holding members 9 to hold the gap between the rear panel 100 and the face panel 200 to the predetermined value. This is because that when the gap between the rear panel 100 and the face panel 200 is changed, the brightness of individual pixels becomes uneven so that it is difficult to obtain a reliable display device. However, the conventional technique is less than optimal with respect to these matters in using the display device in an actual use and these matters constitute drawbacks to be solved.
Accordingly, it is an object of the present invention to provide a display device exhibiting high reliability which can solve the above-mentioned various problems of the conventional techniques and can realize the electron emission characteristics and the high-frequency driving of high performance by adopting a constitution in which a gap formed between cathode wires 2 (electron emitting sources 2a) and control electrodes 4 can be made uniform and a gap formed between a rear panel 100 and a face panel 200 can be held at a predetermined value with high accuracy.